1. Field of the Invention
The present invention relates to a high pressure discharge lamp device with a discharge lamp of the short arc type which is used for a light source of a data projector or the like. The invention relates especially to a reflector of a high pressure discharge lamp device with a superhigh pressure mercury lamp of the short arc type in which the discharge vessel is filled with greater than or equal to 0.15 mg/mm3 of mercury.
2. Background of the Invention
For a light source for projection of data in a projector or the like, there is a need for high illuminance and good color reproduction. Furthermore size reduction of the devices is often desired. In order to meet this demand, superhigh pressure short arc mercury lamps are being used more and more in which the discharge vessel is filled with greater than or equal to 0.15 mg/mm3 of mercury.
However, this type of lamp has a high operating pressure. When the lamps are damaged the problem is in the worst case that lamp fragments spray. Especially for a reflector which is used for a high pressure discharge lamp device with one such lamp a glass component is used with an inside which has been coated with a dielectric multilayer film in order to reflect the light of the lamp with high efficiency. Therefore the problem is that at the same time the lamp is damaged the glass reflector shatters and portions of the glass reflector may fly around.
As a countermeasure against this spraying of lamp fragments the thickness of the glass reflector is conventionally increased, its strength is increased and furthermore a front glass is put in place so that the interior of the reflector has been essentially hermetically enclosed and the spraying of the lamp fragments and the like has been prevented. When the thickness of the glass reflector is increased, the disadvantage however arises that during lamp operation thermal distortion forms and the mechanical strength of the reflector itself is reduced, because the outside of the reflector is cooled and its inside is heated and therefore the temperature difference between the inside and outside becomes large. When for example within an oval reflector of borosilicate glass with a focal length f of less than or equal to 12 mm and a thickness of greater than or equal to 4 mm there is the above described lamp with an input electric power of greater than or equal to 150 W and it is operated at least 1000 hours, in this reflector as a result of the above described thermal distortion there is a high probability that cracks will occur. It was furthermore found that in the case of damage to the lamp it is highly probable that the reflector is also damaged.
As a countermeasure against this spraying of the lamp fragments and the like in the case of lamp damage, a reflector of metal has been used. A metallic reflector in itself however has a low reflectivity. If an attempt is made to coat the metallic reflector with a dielectric multilayer film, as is used for a glass reflector in order to obtain a stipulated reflectivity, the metal surface cannot be directly coated with the dielectric multilayer film. Therefore an intermediate layer of resin or the like must be placed between the dielectric multilayer film and the metallic reflector. This intermediate layer however has very low thermal resistance. Finally, there is the disadvantage that it is difficult to use a metallic reflector.
An object of the present invention is to devise a reflector for a high pressure discharge lamp device in which the reflector is not shattered, or in which when the reflector is broken spraying of the lamp fragments can be prevented with certainty, without increasing the reflector thickness in order to prevent the spraying of the lamp fragments and the like in case of lamp damage.
In accordance with a first aspect of the invention, a reflector for a high pressure discharge lamp device includes a glass reflector wherein there is a discharge lamp of the short arc type in which the discharge vessel is filled with greater than or equal to 0.15 mg/mm3 mercury, and the outside surface of this glass reflector is surrounded with a metal component.
In a further development of the invention the above described metallic component includes is at least one cooling rib.
In the following, the invention is further described using several embodiments shown in the drawings.